CN102502648A - Method for preparing solar grade polycrystalline silicon - Google Patents
Method for preparing solar grade polycrystalline silicon Download PDFInfo
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- CN102502648A CN102502648A CN2011103457744A CN201110345774A CN102502648A CN 102502648 A CN102502648 A CN 102502648A CN 2011103457744 A CN2011103457744 A CN 2011103457744A CN 201110345774 A CN201110345774 A CN 201110345774A CN 102502648 A CN102502648 A CN 102502648A
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Abstract
The invention discloses a method for preparing solar grade polycrystalline silicon, and relates to the field of chemical industry and metallurgy, in particular to a method for preparing solar grade polycrystalline silicon by adopting a metallic reductive silicon tetrafluoride gas. The method comprises the following steps of: a, reduction reaction, and b, melting separation. The purity of the solar grade polycrystalline silicon prepared by the metallic sodium reductive silicon tetrafluoride method can reach over 6N, and the production cost of each kilogram of polycrystalline silicon can be controlled to be 15 to 20 dollars per kilogram. Compared with an improved Siemens method and a silane method for preparing the polycrystalline silicon, the method has the advantages of simple process and supporting facilities, low energy consumption, no discharge of toxic gas, low production and investment costs and the like. Meanwhile, by using silicon tetrafluoride as a main raw material, fluorine and silicon resources serving as byproducts of a phosphate fertilizer can be effectively utilized; and the method provides an effective path for a 'refinement and high addition' thought of the fluorine and silicon resources serving as the byproducts in phosphate compound fertilizers.
Description
Technical field
The present invention relates to chemical industry and field of metallurgy, particularly adopt the metallic reducing silicon tetrafluoride gas to prepare the method for solar-grade polysilicon.
Background technology
Polysilicon is the foundation stone of global electronic industry and photovoltaic industry.2010,8.5 ten thousand tons of Chinese polysilicon production capacities, 4.5 ten thousand tons of actual outputs, 4.75 ten thousand tons of import volumes, import accounts for aggregate demand and surpasses 5 one-tenth.So see from industry actual demand and import figure, there is not over capacity in Chinese polysilicon industry, and domestic supply is still tight slightly.On the other hand, 2006, in the polysilicon output, electronic-grade accounted for 55% in the world, and solar level accounts for 45%, along with the fast development of photovoltaic industry, solar battery chip to the rate of growth of polysilicon demand far above polycrystalline silicon semiconductor.At present; Both at home and abroad adopt of production of polysilicon is Siemens Method and silane thermal decomposition process more, is main to satisfy semi-conductor industry polysilicon demand, silicon for solar cell be adopt produce semi-conductor with the silicon depleted expect end to end, substandard products material and crucible defective material; Purity is more than 6N, but price does not have too big difference.Because output is few, price is high, so the expensive serious development that restricts photovoltaic industry of solar-grade polysilicon material.
At present, about 30～40 dollars/kilogram of most of enterprise production polysilicon costs are produced every kilogram of about 120～150 kWh of the world-class comprehensive power consumption of polysilicon.So the main drawback of traditional technology is expensive, high energy consumption, and there are complex process and problem of environmental pollution.Therefore; The solar-grade polysilicon new preparation technology and the technology of developing low-cost, less energy-consumption; And a solar-grade polysilicon technology for preparing than low-purity comes with the highly purified electronic-grade polycrystalline silicon process distinction of preparation; Further reducing the solar-grade polysilicon cost and become a kind of trend, also is the focus of studying at present.
Chinese patent CN102070144 has announced a kind of method of utilizing the phosphate fertilizer by-product sodium fluosilicate to produce polysilicon, and wherein silicon tetrafluoride is made by the Sodium Silicofluoride 98min thermolysis, adopts tetrahydrochysene aluminium sodium reduction silicon tetrafluoride.There is the low shortcoming with complex manufacturing of transformation efficiency in it.
Chinese patent CN101795964 has announced a kind of method of producing polysilicon, selects for use organic bases to extract the fluorine element silicon in the silicofluoric acid, makes silicon tetrafluoride with sulfuric acid reaction then, adopts magnesium steam reduction silicon tetrafluoride.Its shortcoming is the multiple fertile industrial Sodium Silicofluoride 98min production equipment of phosphorus that needs the reconstruction operational excellence, complex process, and gained silicon purity can only reach 99.99%-99.999%.
Summary of the invention
The objective of the invention is to overcome the defective of prior art, provide a kind of being specifically designed to prepare method low-cost, the less energy-consumption solar-grade polysilicon.
The method for preparing solar-grade polysilicon of the present invention, preparation method are the mixtures that makes Sodium Fluoride and elemental silicon with the tetrafluoride reduced gas of sodium Metal 99.5, behind fusion separation → physical purification, make solar-grade polysilicon; Production equipment mainly comprises Sodium Silicofluoride 98min thermal decomposition furnace, high temperature reduction reactor drum and fusion separator.
The described method for preparing solar-grade polysilicon, its step of preparation process comprises:
The production of a silicon tetrafluoride gas and purification: silicon tetrafluoride gas is made by the thermolysis of phosphate fertilizer by-product fluosilicic acid sodium; The gained silicon tetrafluoride gas is directly or after selecting to purify; Be ready for use on follow-up reduction workshop section, other approach that described silicon tetrafluoride gas is obtained is that making of hydrofluoric acid decomposing metal silicon and sulfuric acid decompose making of fluorite;
The b reduction reaction: place reduction reactor to carry out reduction reaction sodium Metal 99.5 and silicon tetrafluoride gas, reaction zone temperature is 800～1300 ℃, and silicon tetrafluoride gas pressure is 0.01～0.5 MPa;
The c fusion separates: step b gained reaction product is the mixture of Sodium Fluoride and silicon; Mixture gets in the melt and dissolved separator and through the fusion layering reaction product is separated continuously; Wherein silicon is discharged from lower floor, and Sodium Fluoride is discharged from the upper strata, and the fusion separation temperature is 1450～1650 ℃; Silicon after the separation is promptly as the solar-grade polysilicon material, and the sub product Sodium Fluoride can be used as the fluorine chemical raw material;
The d physical purification: step c gained solar-grade polysilicon material is the above solar-grade polysilicon of 6N through processing silicon ingot after vacuum melting, the directional freeze, just obtaining purity further.
Described silicon tetrafluoride gas, purity are 99.9%～99.9999%.
Described sodium Metal 99.5 is the extremely high-purity level of technical grade, and purity is 99.7%～99.9999%.
The described method for preparing solar-grade polysilicon, in the high temperature reduction reaction process, the mol ratio of silicon tetrafluoride and sodium Metal 99.5 is 1:4～1:2.
The described method for preparing solar-grade polysilicon, reduction reactor are divided into top reaction zone and bottom melting zone, and control top reaction zone temperature is 800～1300 ℃, and bottom melting zone temperature is 1450～1650 ℃.
The described method for preparing solar-grade polysilicon, reduction reactor is provided with the liquid metal sodium feed nozzle, and sodium Metal 99.5 is with the charging of fused solution spray form, and feeding temperature is 140～500 ℃.
The described method for preparing solar-grade polysilicon, silicon (Si) that reaction generates and Sodium Fluoride (NaF) all from the reactor bottom melting zone with the fused solution continuous pulp discharge.
The described method for preparing solar-grade polysilicon has liner in the reactor drum, the liner material is a high purity graphite.
The described method for preparing solar-grade polysilicon, the reactor lower part melting zone is provided with heating unit, and heating unit is an induction heating device.
The described method for preparing solar-grade polysilicon, reaction product are in the fusion separator after the fusion layering, respectively with fusion Sodium Fluoride and the continuous discharging of molten silicon.
The described method for preparing solar-grade polysilicon, physical purification are that the solar-grade polysilicon material of preparing adopts vacuum melting and directional freeze casting ingot process purifying.
The ultimate principle of technology of the present invention is: with silicon tetrafluoride gas as the silicon source; Mainly by the thermolysis preparation with sodium fluosilicate, also can be obtained by other technologies as long as satisfy purity requirement, silicon tetrafluoride gas goes out silicon through the active metal sodium reduction; Separate through fusion then, directional freeze makes polysilicon.Wherein, sodium Metal 99.5 gets into reduction reactor with liquid form and silicon tetrafluoride gas is carried out reduction reaction, generates product silicon and by product Sodium Fluoride.Select for use high-temperature melting method that product is separated, and utilize molten silicon and the molten fluoride different and stratified characteristics of not dissolving each other, similar oily water separation with density.In addition, the Sodium Fluoride of generation also can use high purity water or acid solution to carry out the leaching separation.The reaction formula of above-mentioned preparation polysilicon is:
Technical process is as shown in Figure 1, and wherein dotted line is represented nonessential but can be replenished the workshop section of adjustment, and concrete process step is following:
The first step is the preparation and the purification of silicon tetrafluoride gas:
Adopt thermolysis preparation with sodium fluosilicate silicon tetrafluoride gas: Sodium Silicofluoride 98min is delivered to the drying machine inner drying through batch charger, 100 ~ 200 ℃ of drying temperatures.The exsiccant purpose is to remove the moisture content that Sodium Silicofluoride 98min contains, and contains water when preventing the Sodium Silicofluoride 98min thermolysis and produces side reaction.The silicon tetrafluoride that side reaction mainly refers to generate contacts afterreaction with the water vapour in the atmosphere and produces hydrofluoric acid and silicic acid, can cause corrosion to equipment, also influences product purity simultaneously.Dried Sodium Silicofluoride 98min carries out thermolysis under 700～900 ℃ of temperature in thermal decomposition furnace; Produce silicon tetrafluoride gas; Be delivered in the storage tank and store, directly be delivered to the high temperature reduction reactor drum through flow speed controller then, the Sodium Fluoride of generation is collected the back as sub product.
There is the undecomposed situation of small amount of fluorine water glass in the reaction process,, therefore is present in the Sodium Silicofluoride 98min in the sub product Sodium Fluoride, do not influence the silicon tetrafluoride product purity because the purpose of this reaction is to produce the silicon tetrafluoride of gas phase.
Use phosphate fertilizer by-product fluosilicic acid sodium to be raw material, through the prepared silicon tetrafluoride gas of above-mentioned thermal decomposition process, purity is high, particularly contains B, P impurity is low, can directly be used for follow-up reduction workshop section and prepare polycrystalline silicon material.Certainly, in order further to improve final polycrystalline silicon material product purity and quality, can take purifying treatment to silicon tetrafluoride, purification process can be a cryogenic purification, adsorption cleaning etc.
In addition, silicon tetrafluoride gas also can adopt other prepared, as long as satisfy purity between 99.9%～99.9999%, will not detail here.
Second step was that the tetrafluoride reduced gas of sodium Metal 99.5 prepares elemental silicon and by-product Sodium Fluoride:
Active metal sodium is stored in the reductive agent storage tank, and is heated to 140～500 ℃ fused solution, through contactless electromagnetic pump Liquid Sodium is delivered to the high temperature reduction reactor drum.For making reductive agent sodium Metal 99.5 complete reaction, silicon tetrafluoride is excessive, and the mol ratio of control silicon tetrafluoride and sodium Metal 99.5 is between 1:4～1:2.With liquid spray form continuously feeding, sodium contacts the thermopositive reaction of promptly can burning with silicon tetrafluoride to sodium Metal 99.5 after the metering in reduction reactor through the reactor head nozzle.Through indirect cooling water control reaction zone temperature, temperature is controlled at 800～1300 ℃, and reaction produces Si and NaF, falls to the reactor bottom melting zone through gravity.The bottom melting zone is provided with heating unit, and material is heated to 1450～1650 ℃ of molten states, and is implemented in bottom continuous fusion discharge.The high temperature reduction reactor pressure is controlled to be 0.01～0.5Mpa, can control reactor pressure through the silicon tetrafluoride intake and exhaust system.
The 3rd step was to separate HIGH-PURITY SILICON and by product Sodium Fluoride:
High temperature reduction reaction gained S
iWith NaF from reactor bottom melting zone continuous pulp discharge, get in the fusion separator be attached thereto, under 1450～1650 ℃ of conditions, liquid HIGH-PURITY SILICON material is separated with the reaction by-product Sodium Fluoride.Separate and utilize molten silicon and molten fluoride not to dissolve each other and the density different characteristic, the similar oily-water seperating equipment of principle, Sodium Fluoride is walked the upper strata, and silicon is walked lower floor.As long as guarantee that feed composition and feed rate are constant, through the separated product continuous pulp discharge, the height of liquid layer that can control molten materials is constant, realizes the continuous separation of material.Product after the separation is collected in respectively in the high purity graphite container.
Through control raw material silicon tetrafluoride and reductive agent sodium Metal 99.5 purity, the separating obtained polycrystalline silicon material purity of above-mentioned fusion can reach more than 99.9999%, satisfies manufacture of solar cells fully.Why this technology can prepare the high-purity polycrystalline material; Major cause is: (1) is high by the prepared silicon tetrafluoride gas purity of Sodium Silicofluoride 98min thermolysis; Particularly boron (B), phosphorus (P) foreign matter content are very low, wherein contain B≤0.05ppm (wt), contain P≤0.1ppm (wt); (2) impurity in the sodium Metal 99.5 mainly can be divided three classes; One type is the active metal; Like Li, K, Mg, Ca, Al etc.; Even their content very trace also can generate corresponding fluoride salt with silicon tetrafluoride reaction, and get into the Sodium Fluoride phase fully when in reaction process, separating, thereby can not pollute polycrystalline silicon material with fusion; Second type be Fe, Ni, Cu, W, Mo etc. not with the transition metal of silicon tetrafluoride reaction; They can get in the polycrystalline silicon material by trace; But these impurity elements are less to the influence of polycrystalline silicon used for solar battery, and can effectively remove through the follow-up qualitative casting ingot process that solidifies; The 3rd type is that B, P etc. influence bigger nonmetallic impurity to polycrystalline silicon used for solar battery, these components and the trace thereof that contain in the sodium Metal 99.5, and B, P content are all less than 0.1 ppm (wt) in the polycrystalline silicon material that finally obtains.In addition, can be through to the screening of sodium Metal 99.5 material purity or set up online sodium refining plant above impurity is control effectively.
The 4th step was that polycrystalline silicon material is carried out further physical purification:
The difference that possibly exist according to selection and purge cases, technology controlling and process level and clean administrative situation to raw material silicon tetrafluoride and sodium Metal 99.5 purity; For guaranteeing that the prepared polycrystalline silicon material of this technology satisfies the solar cell demand fully, the present invention has replenished follow-up physical purification technology.Physical purification mainly refers to vacuum melting and directional solidification processes, and in the solar energy polycrystalline silicon sheet industrial chain, the inherent polycrystalline silicon casting ingot process can be used fusion and directional freeze, so the physical purification technology of adding can not cause big increase to the cost of the finished product.
In sum, the present invention is equipped with the solar-grade polysilicon material with the tetrafluoride reduced legal system of sodium Metal 99.5, and purity can reach more than the 6N, and its every kilogram production of polysilicon cost can be controlled in 15～20 dollars/kilogram.Compare improvement Siemens Method and silane legal system polysilicon, have that technology and support equipment are simple, energy consumption is low, no toxic gas discharging, a production and cost of investment advantage such as less.Simultaneously, be main raw material with the silicon tetrafluoride, phosphate fertilizer by-product fluorine, silicon resource all can be utilized effectively, and are the effective ways that the multiple fertile enterprise of phosphorus by-product fluorine silicon resource is walked " become more meticulous, high additional " thinking.
Description of drawings
Fig. 1 is the process flow sheet that the present invention prepares the solar-grade polysilicon material.
Embodiment
are done further explanation below in conjunction with accompanying drawing to the present invention, but are not limited to embodiment.
Embodiment 1
A kind of method for preparing solar-grade polysilicon, its step of preparation process comprises:
A. reduction reaction: with sodium Metal 99.5 and purity is that 99.9% silicon tetrafluoride gas places reduction reactor to carry out the high temperature reduction reaction, and silicon tetrafluoride gas is made by the thermolysis of phosphate fertilizer by-product fluosilicic acid sodium, and its pressure is 0.5MPa; Reduction reactor is divided into top reaction zone and bottom melting zone, and control top reaction zone temperature is 800～900 ℃, and bottom melting zone temperature is 1450 ℃; The silicon (Si) that reaction generates with Sodium Fluoride (NaF) all from the reactor bottom melting zone with the fused solution continuous pulp discharge, the reductive agent sodium Metal 99.5 is high-purity grade in the reduction reactor, purity is 99.9999%; In the high temperature reduction reaction process, the mol ratio of silicon tetrafluoride and sodium Metal 99.5 is 1:4, and reduction reactor is provided with the liquid metal sodium feed nozzle; Sodium Metal 99.5 is with the charging of fused solution spray form; Feeding temperature is 140～500 ℃, and liner is arranged in the reactor drum, and the liner material is a high purity graphite; The reactor lower part melting zone is provided with heating unit, and heating unit is an induction heating device;
B. fusion separates: step a gained reaction product is the mixture of Sodium Fluoride and silicon; Mixture gets in the fusion separator and through the fusion layering reaction product is separated continuously; Wherein molten silicon is discharged from lower floor continuously, and the fusion Sodium Fluoride is discharged from the upper strata continuously, and the fusion separation temperature is 1450 ℃; Silicon after the separation is promptly as the solar-grade polysilicon material, and the sub product Sodium Fluoride can be used as the fluorine chemical raw material;
The c physical purification: step b gained solar-grade polysilicon material is the above solar-grade polysilicon of 6N through processing silicon ingot behind vacuum melting, the directional freeze purifying, obtaining purity further.
Embodiment 2
A kind of method for preparing solar-grade polysilicon, its step of preparation process comprises:
A. reduction reaction: with sodium Metal 99.5 and purity is that 99.9999% silicon tetrafluoride gas places reduction reactor to carry out the high temperature reduction reaction, and silicon tetrafluoride gas is made by the thermolysis of phosphate fertilizer by-product fluosilicic acid sodium, and its pressure is 0.01MPa; Reduction reactor is divided into top reaction zone and bottom melting zone, and control top reaction zone temperature is 1200～1300 ℃, and bottom melting zone temperature is 1650 ℃; Silicon (Si) that reaction generates and Sodium Fluoride (NaF) all from the reactor bottom melting zone with the fused solution continuous pulp discharge, the reductive agent sodium Metal 99.5 is a technical grade in the reduction reactor, purity is 99.7%; In the high temperature reduction reaction process, the mol ratio of silicon tetrafluoride and sodium Metal 99.5 is 1:2, and reduction reactor is provided with the liquid metal sodium feed nozzle; Sodium Metal 99.5 is with the charging of fused solution spray form; Feeding temperature is 140～500 ℃, and liner is arranged in the reactor drum, and the liner material is a high purity graphite; The reactor lower part melting zone is provided with heating unit, and heating unit is an induction heating device;
B. fusion separates: step a gained reaction product is the mixture of Sodium Fluoride and silicon; Mixture gets in the fusion separator and through the fusion layering reaction product is separated continuously; Wherein molten silicon is discharged from lower floor continuously, and the fusion Sodium Fluoride is discharged from the upper strata continuously, and the fusion separation temperature is 1650 ℃; Silicon after the separation is promptly as the solar-grade polysilicon material, and the sub product Sodium Fluoride can be used as the fluorine chemical raw material;
The c physical purification: step b gained solar-grade polysilicon material is the above solar-grade polysilicon of 6N through processing silicon ingot behind vacuum melting, the directional freeze purifying, obtaining purity further.
Embodiment 3
A kind of method for preparing solar-grade polysilicon, its step of preparation process comprises:
A. reduction reaction: with sodium Metal 99.5 and purity is that 99.99% silicon tetrafluoride gas places reduction reactor to carry out the high temperature reduction reaction, and silicon tetrafluoride gas is made by the thermolysis of phosphate fertilizer by-product fluosilicic acid sodium, and its pressure is 0.285MPa; Reduction reactor is divided into top reaction zone and bottom melting zone, and control top reaction zone temperature is 1000～1100 ℃, and bottom melting zone temperature is 1550 ℃; The silicon (Si) that reaction generates with Sodium Fluoride (NaF) all from the reactor bottom melting zone with the fused solution continuous pulp discharge, in the reduction reactor reductive agent sodium Metal 99.5 be technical grade to high-purity grade, purity is 99.99%; In the high temperature reduction reaction process, the mol ratio of silicon tetrafluoride and sodium Metal 99.5 is 1:3, and reduction reactor is provided with the liquid metal sodium feed nozzle; Sodium Metal 99.5 is with the charging of fused solution spray form; Feeding temperature is 140～500 ℃, and liner is arranged in the reactor drum, and the liner material is a high purity graphite; The reactor lower part melting zone is provided with heating unit, and heating unit is an induction heating device;
B. fusion separates: step a gained reaction product is the mixture of Sodium Fluoride and silicon; Mixture gets in the fusion separator and through the fusion layering reaction product is separated continuously; Wherein molten silicon is discharged from lower floor continuously, and the fusion Sodium Fluoride is discharged from the upper strata continuously, and the fusion separation temperature is 1550 ℃; Silicon after the separation is promptly as the solar-grade polysilicon material, and the sub product Sodium Fluoride can be used as the fluorine chemical raw material;
The c physical purification: step b gained solar-grade polysilicon material is the above solar-grade polysilicon of 6N through processing silicon ingot behind vacuum melting, the directional freeze purifying, obtaining purity further.
Embodiment 4
According to accompanying drawing 1, Sodium Silicofluoride 98min is delivered to the drying machine inner drying through batch charger, 100 ~ 200 ℃ of drying temperatures, time of drying 2 ~ 3h.Dried Sodium Silicofluoride 98min carries out thermolysis under 700～900 ℃ of temperature in thermal decomposition furnace, produce silicon tetrafluoride gas, is delivered in the storage tank and stores, and directly is delivered to the high temperature reduction reactor drum through flow speed controller then.Simultaneously, use contactless electromagnetic pump that the fused solution sodium Metal 99.5 that is heated to 140～500 ℃ in the reductive agent storage tank is delivered to the high temperature reduction reactor drum, the mol ratio of control silicon tetrafluoride and sodium Metal 99.5 is between 1:4～1:2.With liquid spray form continuously feeding, sodium contacts in reduction reactor with silicon tetrafluoride the burning thermopositive reaction takes place sodium Metal 99.5 after the metering through the reactor head nozzle.The high temperature reduction reactor pressure is controlled at 0.01～0.5Mpa, through the silicon tetrafluoride intake and exhaust system reactor pressure is adjusted.Through indirect cooling water conditioned reaction district temperature, temperature is controlled at 800～1300 ℃.Reaction produces Si and NaF, falls to the reactor bottom melting zone through gravity.The bottom melting zone is provided with induction heating, and material is heated to 1450～1650 ℃ of molten states, and is implemented in bottom continuous fusion discharge.Material gets in the fusion separator that links to each other with reactor lower part, under 1450～1650 ℃ of conditions, liquid HIGH-PURITY SILICON material is separated with the reaction by-product Sodium Fluoride, and Sodium Fluoride is walked the upper strata, and silicon is walked lower floor.Product after the separation is collected in respectively in the high purity graphite container.Gained silicon material makes polysilicon product through vacuum melting after the directional freeze, reach 99.9999% through detecting silicon purity, and the gained Sodium Fluoride is collected the back as sub product.
Above said instance be that the present invention will be described, be not to limit the invention.The present invention requires design, method and the scope protected, all is described in claims of the present invention.Obviously those skilled in the art can carry out various changes and distortion to technology and the device that the present invention makes solar-grade polysilicon and not break away from design of the present invention and scope.Like this, if these modifications of the present invention and distortion are belonged within the scope of claim of the present invention and equivalent technologies thereof, then the present invention also is intended to comprise these changes and is out of shape interior.
Claims (7)
1. a method for preparing solar-grade polysilicon is characterized in that, its step of preparation process comprises:
A. reduction reaction: place reduction reactor to carry out the high temperature reduction reaction sodium Metal 99.5 and silicon tetrafluoride gas; Silicon tetrafluoride gas pressure is 0.01～0.5MPa; Reduction reactor is divided into top reaction zone and bottom melting zone; Control top reaction zone temperature is 800～1300 ℃, and bottom melting zone temperature is 1450～1650 ℃, silicon (Si) that reaction generates and Sodium Fluoride (NaF) all from the reactor bottom melting zone with the fused solution continuous pulp discharge;
B. fusion separates: step a gained reaction product is the mixture of Sodium Fluoride and silicon; Mixture gets in the fusion separator and through the fusion layering reaction product is separated continuously; Wherein molten silicon is discharged from lower floor continuously, and the fusion Sodium Fluoride is discharged from the upper strata continuously, and the fusion separation temperature is 1450～1650 ℃; Silicon after the separation is promptly as the solar-grade polysilicon material, and the sub product Sodium Fluoride can be used as the fluorine chemical raw material.
2. the method for preparing solar-grade polysilicon according to claim 1; It is characterized in that: step b gained solar-grade polysilicon material is the above solar-grade polysilicon of 6N through processing silicon ingot behind vacuum melting, the directional freeze purifying, obtaining purity further.
3. the method for preparing solar-grade polysilicon according to claim 1 is characterized in that: described silicon tetrafluoride gas, purity are 99.9%～99.9999%, are made by the thermolysis of phosphate fertilizer by-product fluosilicic acid sodium.
4. the method for preparing solar-grade polysilicon according to claim 1 is characterized in that: described reductive agent sodium Metal 99.5 is the extremely high-purity level of technical grade, and purity is 99.7%～99.9999%.
5. the method for preparing solar-grade polysilicon according to claim 1 is characterized in that: in the high temperature reduction reaction process, the mol ratio of silicon tetrafluoride and sodium Metal 99.5 is 1:4～1:2.
6. the method for preparing solar-grade polysilicon according to claim 1 is characterized in that: reduction reactor is provided with the liquid metal sodium feed nozzle, and sodium Metal 99.5 is with the charging of fused solution spray form, and feeding temperature is 140～500 ℃.
7. the method for preparing solar-grade polysilicon according to claim 1 is characterized in that: liner is arranged in the reactor drum, and the liner material is a high purity graphite, and the reactor lower part melting zone is provided with heating unit, and heating unit is an induction heating device.
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| CN103395785A (en) * | 2013-07-18 | 2013-11-20 | 贵州省产品质量监督检验院 | Method for preparing polycrystalline silicon by reducing sodium fluosilicate with sodium |
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Application publication date: 20120620 |